MPs are under fresh pressure to let the Commons sleaze watchdog investigate their private lives, it was disclosed today.

The Standards and Privileges Committee has renewed its call for rules to cover all behaviour that "significantly damages the reputation of parliament".

MPs blocked a similar move in March, with Tory Charles Walker warning during a debate that it would result in a focus on "the bedroom and the bottle".

The then Leader of the House, Sir George Young - now Chief Whip - also suggested it could breach politicians' human rights.

As a result the Code of Conduct makes clear that the standards commissioner may not look into allegations relating to members' "purely private and personal lives".

However, in a report today the committee set the stage for another showdown by insisting the situation was "unsatisfactory and uncertain".

"The current position is that either (a) there is no person or body who can consider breaches of the requirement not to undertake any action which would cause significant damage to the reputation and integrity of the House of Commons as a whole, or of its Members generally in relation to actions taken in a Member's personal and private life or (b) that the Committee itself should investigate such allegations.

"We do not consider it appropriate for the Committee to be both investigating and sentencing body."

"It was clear from the debate that some of the difficulty may have been in definition: is, for example, a breach of the law committed in private life a purely personal and private matter?

"Trying to refine definitions simply opens more grounds for argument and challenge, but we consider that the House needs to have the ability to take action in extreme circumstances."

The cross-party group of MPs suggested that the commissioner should be allowed to look into allegations if he had permission from the standards committee.

It is expected to table an amendment to the Code in the House stating: "The Commissioner may not investigate a matter relating only to the conduct of a Member's private and personal life, unless the Committee authorises such an investigation.

"Such investigations shall be authorised only in exceptional circumstances."

Separately, the Commons standards watchdog has set out proposals requiring MPs to declare if their relatives are lobbying the public sector.

Details would have to be included on the register of interests if the politician "is aware, or could reasonably be expected to be aware, of this involvement".

However, guidelines would increase the threshold above which MPs have to list property and land holdings from £66,000 to £100,000.

And they would only need to declare rental income if it was above £10,000 a year.